Under the 3GPP standards, a NodeB (or an eNB in LTE) is the base station via which mobile devices connect to the core network. Recently the 3GPP standards body has adopted an official architecture and started work on a new standard for home base stations (HNB). Where the home base station is operating in accordance with the (Long Term Evolution) LTE standards, the HNB is sometimes referred to as a HeNB. A similar architecture will also be applied in the WiMAX network. In this case, the home base station is commonly referred to as a femto cell. For simplicity, the present application will use the term HeNB to refer to any such home base station and will use the term NodeB generically to refer to other base stations (such as the base station for the macro cell in which a HeNB operates). The HeNB will provide radio coverage (for example, 3G/4G/WiMAX) within the home, small and medium enterprise, shopping Malls etc and will connect to the core network via a suitable public network (for example via an ADSL link to the Internet) or operator network and in the case of the 3GPP standards, via an optional HeNB gateway (HeNB-GW) which typically will aggregate traffic from several HeNBs.
For a HeNB connected behind a HeNB gateway, two pairs of mobile telephone associated connections are established, one between the HeNB and the HeNB gateway, and another between the HeNB gateway and the mobile management entity (MME) within the core network. Mapping between the two contexts associated with a specific mobile telephone is performed by the HeNB gateway, and therefore for a single mobile telephone connected to a HeNB behind a HeNB gateway, context and resources are allocated at both the HeNB and the HeNB gateway.
In common with other NodeBs, HeNBs are able to communicate with each other (and other NodeBs) using the X2 interface. In particular, heNBs are able to coordinate a handover process between source and target base stations using the X2 interface without overall control by the core network. During an X2 based handover between two HeNBs, the target HeNB explicitly releases the UE context at the source HeNB using the X2AP UE Context Release procedure. However, as the X2 interface is used to coordinate the handover, for a source HeNB behind a HeNB gateway, no message relating to release of the UE context traverses through the HeNB gateway, and therefore the HeNB gateway does not have any means to understand the mobile telephone has been handed over via an X2 based handover to the target HeNB.